The present invention relates to brominated and epoxidized compounds and to the use thereof as flame retardants for organic polymers such as polymers and copolymers of styrene. The invention also relates to certain processes for preparing brominated and epoxidized compounds.
Brominated compounds such as hexabromocyclododecane are commonly used as flame retardant (FR) additives for various polymer systems. FR additives improve the performance of polymer systems in standard fire tests. Because hexabromocyclododecane is under regulatory and public pressure that may lead to restrictions on its use, there is an incentive to find a replacement for it.
Among the candidates for replacing hexabromocyclododecane are higher molecular weight (1500 or greater) brominated compounds and polymers. The higher molecular weight of these materials tends to greatly restrict their bioavailability, and for that reason these materials are not expected to bioaccumulate.
Most organic polymers are made into useful products via some melt-processing operation in which the polymer is subjected to temperatures that are high enough to melt it. In many polymer melt processing operations, the FR additive may be exposed to temperatures of 200 to 250° C. or higher. The FR additive must possess sufficient thermal stability to undergo very little, if any, thermal degradation when subjected to those melt processing conditions.
Brominated FR additives are believed to function by evolving HBr when the additive is exposed to temperatures in excess of about 300° C. Unfortunately, HBr tends to evolve even at temperatures as low as 180° C. in some cases. The HBr that evolves tends to catalyze the evolution of more HBr as well as other unwanted reactions such as cross-linking, which can lead to gel formation. Even a small amount of HBr evolution can be a significant problem, due to the auto-catalytic effect that the liberated HBr has on the system.
For this reason, polymer systems that contain brominated FR additives often contain an HBr scavenger. Epoxide compounds are commonly used for this purpose. However, this requires an additional material to be compounded into the organic polymer, which adds raw material costs and often adds additional compounding costs.
Another problem is that the epoxide additives may perform less effectively as higher molecular weight brominated FR agents replace hexabromocyclododecane. This may be due to solubility issues. Higher molecular weight brominated FR additives are often significantly less soluble in the organic polymer matrix than is hexabromocyclododecane. For example, one potential replacement of interest, a brominated butadiene-styrene copolymer, tends to disperse in polystyrene in the form of small but discrete particles. The epoxide compound, on the other hand, usually is soluble in the polystyrene phase. It may for that reason partition between the polystyrene and brominate copolymer phases. The portion of the epoxide compound which partitions into the polystyrene is not in intimate contact with the FR additive and may function less effectively for that reason.